Signaling system



June 1 1926.

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June 1 1926.

A. M. CURTIS SIGNALING SYSTEM- ma i 3 k NQ WM V QM Mm mww I #21 9/720/1' Ausfcw M Cur/73 June 1 192s. 1,586,970

A. M. CURTIS S IGNALING SYSTEM Filed Feb. 5, 1924 5 Sheets-Sheet 5 lflllllll II lilllllP 304 I y l I 1 I I l mwmo x Y Aus/en M Cur/As Patented June 1, 1926.

. UNITED STATES,

PATENT OFFICE-i AUSTEN M. CURTIS, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC 7 COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK- [SIGNALING SYSTEM.

Applicationfiled February 5, 1924. Serial No. 690,709.

This invention relates to submarine telegraph signaling and more particularly to signal amplifying and wave shaping.

The objects of the'invention are to accomplish proper shaping of Signals transmitted over a submarine cable adapted for high speed operation and to efficiently and economically amplify or boost the signals at intermediate repeating stations.

The profit from a submarine cable depends upon the number of messages which can be sent through it intelligibly' and the initial, investment is very great. Much effort has, therefore, been put forth in attempts to improve the cable or the terminal apparatus in such a way as to permit of increased speed of signaling. A very great step inadvance has recently been made by the discovery of a nickel iron alloy, called permalloy, which has a remarkably high permeability at the low magnetic forces involved in signaling, and other properties which, it is discovered, peculiarly fit it as a material for inductively loading submarine cables. This improved loading, when applied to transoceanic cables, will permit signaling speeds to be increased many times. For a complete description of this magnetic material and its application to loading of submarine cables, see U. S. applications of G. W. Elmen, Serial No. 473,877, filed May 31, 1921 and O. E. Buckley, Serial No. 492,- 725, filed August 16, 1921.

It is customary in submarine telegraph operation to signal by impressing positive and negative impulses upon the cable in various combinations and there will always be some limiting frequency of transmitted impulses above which the received signals will 'be unintelligible. This limiting frequency may be called the limiting signaling frequency and is expressed in cycles per second. By signaling frequency is meant the number of dot impulses transmitted per second when a succession of alternate dot and dash impulses is sent at the designated frequency of operation.

In transmitting cable telegraph signals, various combinations of positive and negative impulses with periods of zero current are employed so that theoretically the trans mitted currents may have frequency components anywhere within the range from zero to infinity. Inorder to obtain sufliciently well-formed signals at the receiver, such a wide range of frequencies is not actually required. Satisfactory results may be obtained providing all of the component frequencies up to about one and a half times the signaling frequency are properly trans.- mitted. Thus, for signaling frequencies of 10 to or cycles, it is important to trans mit frequency components up to about 100 cycles. It is obvious that for higher signaling frequencies higher frequency components will need to be transmitted.

This invention is the result of a careful investigation of the factors affecting submarine cable signal transmission at signaling speeds in the range extending upward from those heretofore commercially used and involving frequencies up to several hundred cycles per second. Certain features of the invention, however, are useful also in other frequenc ranges, as will appear from the descriptions given below.

It is well known that electron discharge devices may be used to amplify submarine cable signaling currents and that electrical networks may be used to vary the wave form of such currents. In this connection, reference may be had to British Patent No. 153,- 357 and U. S. Patent to B. W. KendallNo. 1,453,982, May 1, 1923.

There are several aspects to the invention.

In one aspect, the invention comprises a complete submarine cable telegraph system i in which novel means for shaping and amplifying message currents are employed.

Sending, repeating, and receiving apparatus is involved.

In another aspect, the invention relates to shaping means which acts primarily to effect relative phase shifts of the component freshunt thereof, each properly proportioned posite directions for improving the oper-.

ation of a mid-circuit repeater.

Still another feature closely related to the mid-circuit repeater, but which is important from the standpoint of economical operation of the system as a whole, invo- Jes the adjustment of a mid-circuit repeater in such a manner asto correct in part only for unequal. distortion of difi'erent signal frequencies caused by the transmission circuit, thereby economizing in power and reducing the cost of the apparatus, without at the same time requiring careful adjustment and readjustment.

The novel features which are considered characteristic of this invention are set forth with particularityin the appended claims. The invention, both as to its organization and method of operation together with other objects and advantages thereof, will be further explained by reference to the following description taken in connection with the accompanying drawing consisting of the following figures: Fig. 1 illustrates schematically a duplex cable telegraph system employing a multistage electron discharge amplifier at the receiving terminal, wherein the wave shaping network precedes the first stage.

Fig. 2 shows another type of multi-stage amplifier, wherein a highly damped selective circuit is used between the first and second stages.

Fig. 3 shows another multi-stage amplifier somewhat like that of Fig. 2 but employing both adifi'erent type of electron discharge device and a different type of coupling between stages.

Fig. 4 illustrates another duplex cable telegraph system employing a specially shielded bridge .transformer and highly damped selective circuits between all stages. grounding arrangement is also illustrated.

Fig. 5 shows another type of amplifier similar to that of Fig. 4. but..employing a difierent size of discharge device -Fig. 6 shows a modified type of amplifier in which the wave shaping networks are connected in the inputcircuits of the several electron discharge devices.

Fig. 7 shows a type of recording device suitable for use with terminal amplifiers.

.Fig. 8 illustrates a two-way mid-circuit repeater.

Figs. 9, 10 and 11 show various schematic views of a specially shielded bridge transformer. Fig. 12 shows a portion of a submarine cable telegraph system adapted to be used with the arran ement of Fi 6, especially suitable for big submarine cables.

The arrangements shown in the several figures will now be described in detail. It will be, noted that the detailed descriptions follow closely the orderly procedure of the lnvestigation hereinbefore mentioned, and proceed from arrangements primarily adapted to the lower speeds of the range of signaling speeds involved to the arrangements which make possible the use of the higher speeds. Reasonable values will be assigned to the several elements to enable those skilled in the art to readily practice the invention but it is to be understood that the invention is not to be limited to the particular values given.

Referring now to Fig. 1, a cable 5 is provided with terminal apparatus for duplex operation. :At terminal X, an inverted bridge system is employed comprising resistance arms 6 and 7 of 500 ohms each and artificial balancing cable 8 to balance the electrical characteristics of cable 5. Both the artificial balancing cable 8 and cable 5 have a KR constant of 2.24. The sending apparatus, represented conventionally by battery 9, keys 10 and 11 and resistance 12 at S, is shown connected across conjugate points of the duplex bridge. The receiving amplifier RA is connected through a selective network 13 to the apex 16 of the bridge. Signaling is accomplished in a well known manner, positive impulses being transmitted to the cable 5 by the closure of dot-key 10 on contact 14 and negative impulses by the closure of dash-key 11 on contact 15.

This duplex arrangement permits of using a grounded amplifier directly connected to speed signaling over loaded the duplex bridge without a bridge transformer. Under certain conditions, this arrangement is advantageous in'provi'ding a practical operating system.

' At terminal Y, only the sending apparatus is shown and this in conventional form.

The equipment at terminal Y may be identical with that at terminal X.

The selective network 13 consists of a variable condenser 17 of 5 to40 microfarads capacity connected in series between the apex '16 of the duplex bridge and thegrid of the of condenser '17 consists of an inductance coil 190i 4 to 20 henrys and a variable resistance 20 of zero to 150 ohms. The circuit connected to the right-hand terminal of condenser 17 consists ofan. inductance coil 21 of 1 henry maximum inductance and a resistance 22 of zero to 100 ohms.

The four amplifying devices 1A1, 1A2, 1A3 and 1A4 are resistance-coupled in tandem. The filaments are heated from battery 23 of six volts. Space current is supplied from batteries 1B1, 1B2, 1B3 and 1B4, one for each amplifier and each of 150 volts. In series with batteries 1131 and 132 are resistances 24 and 25 each of 200,000 ohms. In series with battery 1B3 is a resistance 26 of 50,000 ohms. The condensers 27 between stages are each of 9 microfarads capacity. The input circuits of amplifiers 1A2, 1- 3 and 1A4 are each shunted'by a leak resistance 28 of two megohms. A negative polarizing source of potential 29 is supplied for the grids of each of the amplifiers, the values of these potentials being 1.5 volts for amplifiers 1A1 and 1A2, three volts for 1A3 and eight volts for 1A4.

Connected to the output'circuit of the last amplifier 1A4 across a variable resistance 31 of 300 to 2000 ohms is a recording device R represented as a coil" which may be of any suitable form, such as an oscillograph or siphon recorder. A battery 30 of from 4 to .40 volts is connected in series with the recorderR to neutralize the drop in potential through resistance 31 corresponding to the zero signaling current condition.

The amplifier- RA 'is substantially distortionless and any change in the Wave form of the arrival current is effected by theselective network 13-.

Commercial vacuum tubes manufactured v by Western Electric Company, Incorporated, are suitable for the amplifiers. Those designated at No.209-A are preferably for amplifiers 1A1 and 1A2, those designated as No. 203B for amplifier 1A3 and those designated at No. 210A for amplifier 1A4.

The arrangement of Fig. 1 permits of signailing at about 10 cycles per second provided the unbalance is kept below 0.1 millivolts. If the unbalance is greater than this,

i a somewhat reduced signaling frequency is necessary.

- Referring now to Fig. 2, a somewhat different type of receiving amplifier RA is employed. Thednput circuit of amplifying device 2A1 is connected to the apex 16 of the duplexbridge and is shunted by a single circuit 39 comprising an inductance coil 40 of 4 to 20 henrys and a variable resistance '41 of zero to 150 ohms. This circuit is identical with the circuit at-the left-hand side of condenser 17 in Fig. 1. I v

'The first two amplifying devices 2A1 and 2A2 are coupled in tandem through a selective network 42. a The second and third amplifyin devices 2A2 and 2A3 are resistancecouple in tandem.' The filamentsof all of the, amplifying devices are heated from a potentials being battery 43 of six volts. Space current is supplied from batteries 2B1 of 120 volt-s, 2B2 of 160 volts and 2133 of 150 volts.

In. series with battery 2B1 is a variable resistance 44 of zero to 200,000 ohms and an inductance coil 45 of 20,000 henrys maximum inductance. The plate of amplifying device 2A1 is connected to an intermediate po nt of inductance COll 45. The inductance of the portion of the coil between the resistance 44 and this tap is about ($00 henrys.

the variable condenser 47 and the other. va-

riableelements.

In series with the battery 2132 is a resistance 49 of 100,000 ohms. The condensers 50 connected between stages are each of 9 microfarads capacity. The input circuitsof amplifying devices 2A2 and 2A3 are each shunted by a leak resistance 51 of 2 megohms. A negative polarizing source of potential 52 is supplied for the grids of each of the amplifying devices, the value of these 1.5 volts for amplifier 2A1, 3 volts for amplifier 2A2 and 10 volts for Connected to the output circuit of the last amplifier 2A3 across a resistance 53 of 500 to 2000 ohms is a recording device R similar to I The elements of network wave shape of the arrival current being changed both in the net work preceding amplifier 2A1 and the network 42 following amplifier 2A1.

Commercial vacuum tubes manufactured by estern Electric Company, Incorporated, are also preferred for the amplifiers of Fig. 2, those designated as N0.,209-A being preferred for amplifiers 2A1 and 2A2 and No. 210-11 for amplifier 2A3.

In the arrangement of Fig. 2, much higher speeds can be employed. Speeds as high as 15 cycles per second can be used and when working full duplex a local sending speed of 10 cycles per second is possible when no component of the unbalance exceeds 0.2 milli-volts with a local sending battery of 60. volts.-

Referring now to Fig. 3, still another type of multi-stage amplifier is shown. The apex 16 of the duplex bridge is connected to a potentiometer 60 of 40,000 ohms. Bridged across this potentiometer is a shaping network 61 consisting of a variable inductance coil 62 of 2 to 8 henrys and a variable resistance 63 of zero to 150 ohms. The four amplifying devices 3A1, 3A2, 3A3 and 3A4 are tandem connected through shaping networks 64, 65 and 66. The filaments are heated from a battery 67 of two volts. Space of inductance coil 70. A variable condenser 71 of .001 to .02 microfarads is connected in shunt of both the inductance coil and the resistance 69. The networks 65 and 66 each consist of a variable resistance 72 of zero to 29,000 ohms and an inductance coil 73 of 400' henrys. The grids of the several amplifiers are maintained at the proper potential with respect to the filament by means of potentiometers 74 each of 20,000 ohms resistance and batteries 75 of 1.5 volts. It is to be noted that the batteries? 5 for amplifiers 3A2, 3A3 and 3A4 have their positive terminals connected toward the grids. This is necessary to partially neutralize the high negative potential which would otherwise be impressed upon the grids due to the drop of potential in resistances 69 and 72, due to flow of space current therein.

Connected to the output circuit of the last amplifier 3A4 across a resistance 76 of zero to 20,000 ohms is a recording device R. Due to-the relatively low current of battery 68, no neutralizing battery is connected in series with this recorder. The zero position of the recorder may be adjusted by biasing the recorder suspension.

Commercial vacuum tubes manufactured by Western Electric Company, Incorporated, designated as No. 215A are preferably used in allthe stages. For the amplifier.3A4,.two of these vacuum tubes connected in parallel are preferred, although one only is illustrated in the drawing for the sake of simplicity. The arrangement of Fig. 3 permits of about the same speed of signaling asthat of Fig. 2. Both the space occupiedby the ap- -paratus and the battery consumption is,

however, very much reduced. The shaping adjustments are also much simplified so that an operator, even though unacquainted with the circuit arrangement and guided only by a single sheet of written instructions, is able to shape the signals satisfactorily at a speed of 10 cycles per second in'fifteen minutes time.

Referring now to Fig. 4, another type of duplex cable telegraph s stem is illustrated employing a specially shielded bridge transformer so that both the sending battery and the receiving amplifier may be grounded. In this arrangement, cable 5 and artificial cable 8, together with condensers 80 and 81, form an ordinary duplex bridge. Sending apparatus S is connected to the apex of the bridge through an adjustable slide wire re- 'sistance 82. Variable resistances 83 are provided for adjustment of the cable and artificial cable arms of the bridge respectively. Connected across the conjugate points of the bridge is a shaping network 84 similar to the network 39 of Fig. 2 but having a shield 85. To these same conjugate points of the bridge is connected the primary winding of the specially shielded bridge transformer 86. The shield 87 whichsurrounds the primary winding is connected to one terminal of the primary winding, while the shield 88 which surrounds the secondary winding is connected to ground. Further details of construction of this transformer will be given hereinafter in connection with the further description of Figs. 10, 11 and 12.

The amplifier in this arrangement consists of two sections. When it is desired to operate a recorder R only, the section RA consisting of four stages is provided. If it is desired on the other hand to operate a telegraph relay, a relay receiving amplifier ERA consisting of two stages is added.

The amplifier RA preferably employs the same type of vacuum tubes as are preferred for the ar'rangementof Fig. 3,-namely,

those manufactured by Western Electric Company, Incorporated, and known as No. 215-A vacuum tubes.

The secondary of the shielded transformer 86 is closed on a potentiometer 122 of 1,000,- 000 ohms resistance, for convenience in adjusting the strength of the signals. The middle contact ofthe potentiometer is connected to a grid polarizing potentiometer 89 of 20,000 ohms. This potentiometer '89 is shunted by a battery 90 of 4.5 volts so connected that the effect upon the grid of amplifier 4A1 will be to make it more negative than the filament. The middle. contact of the grid potentiometer 89 is connected through a resistance 91 of 10,000 ohms to the grid of amplifier 4A1. Connected between the grid of amplifier 4A1 and the filament is a condenser 92 of .001 microfarads capacity by the shortest possible leads. Resistance 91 and condenser-92am provided to prevent a rectification and trans mission through the amplifier 4A1 of high frequency interference such'as is picked up from sparking at contacts," etc. This feature is fully described and claimed in applica-nts copending application, Serial No.

679.315, filed Dec. 8, 1923. The filament circuits of the amplifiers 4:A1,'4A2, 4A3 and 4A4 are all connecte' in I parallel and supplied with current from attery 93 of two volts. The plate of amplifier 4A1 is connected through battery 94 of volts to an intermediate point of inductance coil 96, the maximum inductance of which is 10,000 henrys. Between the lower terminal of coil 96 and ground is connected a variable resistance 97 having a maximum value of 100,000 ohms. Bridged across the coil .96.

and the resistance 97 is a variable condenser 98 of .001 to .040 microfaradscapacity. This condenser assists materially inshaping the signals and reducing the effect of interferences and unbalance. Y

Coil 96 is preferably made up as follows: The core is of the form hereinafter to be described in connection with bridge transformer 86 and consists of 6 mil permalloy with a minimum practical air gap. The nature of the permalloy material employed is described in an article by Messrs. Arnold and Elmen entitled Permalloy, an alloy of remarkable magnetic properties which was published in the Journal of the Franklin Institute volume 195 No. 5, May 1923. The windings on each core consist of three 0.25 inch sections 0f 5000 turns of No. 40 single silk covered copper wire each and two 0.35 inch sections of 7000 turns of No. 40 single silk covered, copper wire each.

The coil construction just described provides a coil of. relatively high natural frequency compared with that of the frequencies involved in submarine cable telegraphy. In combination with such a coil, it is therefore possible to use-a condenser, such as condenser 98, to.provide a highly damped selective circuit ,99, consisting of inductance coil 96, resistance 97 and condenser 98, which circuit is most effective at a desired frequency within or somewhat above the range of frequencies essential to the reproduction of the signals, and is less effective to neighboring frequencies by any desired amount.

The advantages of the use of permalloy which permits of the construction of a coil having a high natural frequency are not. limited, however. to the relatively low frequencies involved in submarine cable telegraphy, but are also applicable to coils designed for any other ranges of frequencies. The natural frequency of an inductance 'coil depends both upon the inductance and the equivalent shunt capacity. If the value of the inductance, determined by circuit conditions, must be larger than a certain minimum value,, the highest natural frequency which can be obtained is limited by the amount to which the shunt capacity. can be reduced. The shunt capacity in turn is determined by the number ofturns required to give the minimum value of inductance. According to this invention permalloy is used for the magnetic circuit, of an inductance coil thereby making possible a coil of the required inductance value with'a lower shunt capacity and therefore a higher natural frequency than previously known in the art.

The use of coils having, permalloy cores is especially valuable in submarine cable telegraphy because of the large values of inductances required in the coils of the shaping networks and the low values of the frequencies to which these networks must be adjusted.

The high voltage side of coil .96 is also connected to the grid of amplifier 4A2 through'potentiometer 89 and resistance 91 which are the same in all stages. Each of the amplifiers isprovided with a condenser 92. of the same size and for the same purpose as condenser'92 of amplifier 4A1. It is to be noted that the grid polarizing batteries in the second and succeeding stages are connected with their positive sides toward the grids as was the case in the arrangement of Fig. 3 and for the purpose described in connection with that figure.

The coupling between amplifiers 4A2 .and 4A3 and between 4A3 and 4A4 are similar to that between amplifiers 4A1 and 4A2. The same type of inductance coil 96 and resistance 97 is employed.

The interstate networks 100 and 101 following the second and third stages are similar to network 99 of the first stage. The condenser 102 with its resistance 103, and

condenser l04= with its resistance 105, co-

the amount of interference received at fre-- quencies above the'signaling range.

The amplifier 4A4 of the fourthstage consists preferably of two No. 215A vacuum tubes connected in parallel although only one is shown for the matter of convenience. A switch 106 is used to connect the output circuit of amplifier 4A4 with either recorder R or the input circuit of amplifier REA. When connected to the recorder R, as shown, the plate circuit of amplifier 4A4 passes through battery 107 of, 50 volts, [a resistance 108 of 1000 to 10,000 ohms and the coil of recorder R shunted by resistance 109 of 1000 to 30,000 ohms. Resistance 108 is adjusted to the lowest valve which permits good signals, its purpose being to straighten out the curved characteristic of amplifier tubes 4A4 and to reduce modulation of the signal by the motional impedance of the recorder. of adjusting the dampingof therecorder.

Resistance 109 is for the purpose The bias of the recorder caused by the space current is corrected by amechanical adJustment of the recorder suspension.

When the amplifier is to be used to operate relays, larger currents are required and the resistance-coupled distortionless amplifier RRA is therefore provided. This amplifier may be connected to the output circuit of the last stage of amplifier RA by throwing switch 106 to the right. In this position, the output circuit of amplifier 4A4 including battery 1-07 is closed through a resistance 110 of 20,000 ohms. In order to overcome the drop in otential through the resistance 110, an extra attery 111 of 50 volts is connected in series with battery 107.

The negative potential at the upper terminalof resistance 110 caused by the voltage dro across the resistance 110 is compensated y a positive grid battery 112 which leaves the grid of am lifier 4A5 about five volts negatlve. The p ate of am lifier 4A5 is con led to the grid of amp ifier 4A6 throng resistance 113 of 10,000 ohms, condenser 114 of microfarads, leak resistance 115 of two megohms and negative id po- TIi e plate larizing battery 116 of volts.

circuits of amplifier 4A5 and 4A6 are supplied from the same source, namely, battery 117 of 150 volts. The late circuit of amplifier 4A6 includes resistance 118, of 2000 ohms, the function of which is to prevent the variable impedance of relay REL from modulating the signal unfavorably. It alsoassists in preventing distortion by straighten ing the characteristicof amplifier 4A6. The field in the relay REL due to the normal non-marking plate current of amplifier 4A6 is compensated by a similar field in the sep arate winding 119. This field is adjusted by means of resistance 120 whosevalue depends upon the constants of the windings of the relay used. The filaments of both stages are heated by battery 121 of eight volts.

The preferred types of vacuum tubes are those of Western Electric Company manu facture, No. 208A vacuum tubes being used for amplifier 4A5 and No. 210-A for amplicircuitelements, which are to be connected to ground or to the positive terminal of bats tery 93, is so connected through separate .leads instead of to a common bus bar as is customary. This type of connection is very important in these systems due to the small received currents involved and to the necessity for preventing reaction between stages. and other interference. While this arrangement of wiring is equally important in all of the systems illustrated, for the matter of simplicity it has been shown onlyin Fig. 4.

From the detailed description given of the preceding figures, it is only necessary in the following description to give the preferred values for the several circuit elements and to point out wherein the arrangements differ from 'those already described.

In the arrangement of Fig. 5, another type of amplifier, similar to that of Fig. 4 but ernployin a difi'erent type of vacuum tube an a di erent type of interstage coupling, is shown. The duplex bridge and bridge transformer circuits are the same as those in the arrangement of Fig. 4 as is also the input potentiometer 130. Pick-up prevention condensers 131 and resistances 132 are used in the first threestages. The plate of amplifier 5A1 is connected to the intermediate point of inductance coil 133 which may be the same as coil 96 of Fig. 4. The lower side of coil 133'is connected to the positive side of battery 5B1 of 150 volts through a variable resistance 134, having a maximum value of 100,000 ohms. Bridged across inductance coil 133, resistance 134 and battery 5131 is a variable condenser 135 of 0.001 to 0.040 microfarads capacity. The upper terminal of coil 133 is also connected to the grid of amplifier 5A2 through a condenser 36 of 10 microfarads capacity, a leak resistance 137 of 2 megohms,-a negative grid polarizing battery 138 of three volts and a pick-up interference preventer resistance 132 and condenser 131.

The plate of the second stage amplifier 5A2 is connected to the midpoint of inductance coil 139 whose lower point is connected to the positive terminal of battery 5B2 also of 150 volts through resistance 140 of 100,000 ohms maximum. The upper side of inductance 139 is connected to. the grid of amplifier 5A3 through a condenser 141 of 10 microfarads, the negative polarizing battery 142 of six volts, leak resistance 143 of two megohms and pick-up preventer resistance 132 and condenser 131. A variable condenser 144 and variable resistance 145 shunted from the upper terminal of inductance coil 139 to ground are adjusted to values which reduce high frequency interference -without afi'ecting'the signal.

When the recorder R is used, the plate of amplifier 5A3 isconnected to the high side ofthe step-down auto-transformer 146 and through it and resistance 147 to the positive terminal of battery 5B3 of 150 volts. The auto-transformer 146 is preferably of 500 henrys inductance. The drop of potential across resistance 147 is balanced by the compensating battery 148 of appropriate voltage and by the potentiometer149 as it is not permissible to allow current of: more than about 500 micro amperes to flow through the recorder coil R.

When the amplifier of Fig. 5 is used to operate a relay, the plate of amplifier 5A3 is connected to an intermediate point of coil 150 by moving switch 151 to its upper posi resistance 154' which are respectively the same as condenser 144 and resistance 145 and tunction 1n the same manner. The upper terminal of coil 150 18 also connected to the grid of amplifier 5A4 through condenser 155 of 10 microtarads capacity, a leak resistance 156 of two niegohms and a negative polarizing battery 157 of 15 volts. The plate of amplifier 5A4 is connected through one winding of the relay REL and resistance 158 to the positive side of battery 5133. Resistance 158 is for the purpose of preventing the change in impedance of the relay from modulating the signal wave. The field of the relay due to the normal plate current of amplifier 5A4 is neutralized by the field established through winding 159 which current is regulated by variable resistance 160.

The filaments of the tubes are heated by battery 161.

In the arrangement of Fig. 6, an amplifier is shown which is especially adapted to operate at high speeds up to a signaling frequency of 60 or more cycles per second. This amplifier is somewhat similar to that of Fig. 5. As illustrated, the amplifier of Fig. 6 is adapted to operate a recording device, such as a siphon recorder or oscillograph, but additional stages of amplificationcould be added in the manner illustrated in preceding figures. The first stageis shown connected directly to the cable 5 which is suitablefor simplex operation but it could, of course, be connected to a duplex bridge in the manner illustrated anddescribed in connection with the preceding figures.=y I Connected between the cable 5 and is a potentiometer 180 of 6,000 ohms. Bridged across the potentiometer 180 is a shaping network 61 similar to network 61 of Fig. 3, and comprising inductance coil 62 and resistance 63. The intermediate terminal of potentiometer 180 is connected through a resistance 181 of 12,000 ohms and negative grid polarizing battery 182 of two volts to the grid-of amplifier 6A1. Condenser 183 of .0005 microfarads capacity is connected by means of the shortest possible leads from the grid to the filament o't' amplifier 6A1 and in cooperation with resistance 181 prevents pick-up interference. The out put circuit of, amplifier 6A1 is coupled to shaping network 184 by means of resistance 185 of 200,000 ohms and condenser 186 of 22 microfarads capacity. In series-with resistance 185 is space current supply bat.- tery 6B1 of 250 volts. The shaping network 184 consists of a variable condenser 187 of ground 0.01 to 0.19 microfarads capacity, an adof (3,000 henrys maximum inductance and a copper resistance of 54,000 ohms. The design features of this inductance coil will be given hereinafter. The upper terminal of coil 189 is connected to the grid of amplifier 6A2 through a variable resistance 190 of two megohms maximum resistance and a negative grid battery 191 of three volts. A condenser 192 of 0.001 microfarads capacity cooperates with resistance -190 to prevent pick-up interference in the manner hereinbetore described, and also assists in shaping the signals and suppressing high frequency interference.

It is to be noted that the shaping network 184 is connected in the input circuit of the succeeding amplifier, thereby differing from the arrangements previously described. By this connection, space current of the preceding tube is prevented from flowing in the inductance coil of the shaping network and higher potentials may consequently be impressed upon the plate of the preceding tube without producing deleterious effects upon the wave shaping network. By means of condenser 187 ,the highly damped selective network 184 may be made most effective at any desired frequency so as to accentuate those frequencies of the signaling current which are most highly attenuated during transmission and to reduceintert'ering frequencies.

Amplifier 6A2 is coupled to shaping network 193 by means of resistance 194 of 200,000 ohms and condenser 195 of 6 microfarads capacity. In series 194 is space current battery 6132 of 250 volts. The network 193 consists of an inductance coil 196 adjustable to a maximum inductance 'of 100 henrys, a condenser 290 adjustable with resistance condenser 290 is connected across a 2 inegohm grid leak resistance 198 for tube (3A3 and'thus forms a shunt from the grid of that tube to the ground.

Amplifier 6A3 is similarly coupled to shapingnetwork 202 by a resistance a 'condenser 201. sists of an adjustable inductance coil 203, a variable condenser 291, and a variable resistance 204.-' The coil 203 and the resistance 204 are in parallel with each other and, in series with the coupling condenser 201, are

connected between the plate of tube 6A3 and the grid of tube 6A4.

connected across agrid leak resistance 205 I The condenser 291 is 200 and Shaping network 202=con-' for tube 6A4 and thus forms a shunt from the grid of that tube to the ground. A battery 6B3 supplies space current for tube 6A3. The output circuit of tube 6A4 is connected through a battery 7 B4 to a recorder R.

The recorder B may be a high speed siphon recorder shown schematically in Fig.

i. The movable coil 210 is shunted by variable resistance 211 of 60 to 1200 ohms. The field coil 214 is energized by current from battery 212 under the control of a suitable resistance 213. The bias of the movable coil, dueto normal flow of plate current thcrethrough during non-marking condition, can be neutralized by adjustment of the suspension or bya separate battery as ex.

plained in connection with Fig. 1.

The functions performed by the different portions of the circuit arrangements of Fig. 6 will now'be explained more in detail. It happens that with the telegraph signal waves as received from most cables-terminating in magnetic shuntsv of the usual type, the shunt being properly adjusted, the varione frequency components which go to make up the signals are nearly in proper phase re-, lationship. The shaping amplifier exclusive of the magnetic shunt serves, Without introducing on its own account such relative phase shifts of the different frequencies as would have important effect upon the shape of the signal wave, to correct'for the unequal attenuations experienced by the different frequency components in the cable, .to eliminate disturbances of frequencies higher than those necessary to compose the signal,.'and

to bring up thesignal to suitable indicating magnitude.

The four amplifying stages of the shaping amplifier divide it into four parts; the first comprising the cable termination including the magnetic shunt 61 and the second the network 184 between the first two stages. This network with the magnetic shunt does the principal shaping. The coil 62 and its associated resistance 63 are the principal quencies in traversing the cable, it is necessary to take into account a fairly wide range of frequencies. extending from a very low limit to a frequency perhaps one and onehalf times or more the signaling frequency. For example, if the signaling frequency is 60 cycles, it is desirable to-give correcting attention to all frequencies from perhaps 90 cycles down to a quarter of a cycle. The low frequencies become of importance when line conditions remain unchanged for a time, as when the sending operator changes a tape, the operation requiring perhaps one second- During this time the receiver should stay at its normal'operating zero position and not wander off to a false starting position where it might give an incorrect indication when actual signals commence to come through again. If a longer time is required a series of reversals should be sent to clear the cable before commencing to send signals. This means that the amplifying system must operate on frequencies very nearly down to zero, that is, direct current.

As previously stated, for most cables the magnetic shunt 61 very nearly corrects for phasedisplacement of the wave components of. the received-signals. The principal waveshaping, that is, about two-thirds of it, is

preferably accomplished by shaping network184 between the first and second stages. The two subsequent interstage networks 193 and 202 may actually impair the-signal so far as its shaping is concerned but serve another essential functions, as mentioned above and explained hereinafter.

Returning to the principal wave shaping network 184, the 200,000 ohmresistance 185 insures a straight line characteristic of the first stage amplifier 6A1 and adequate potential differences at the low frequencies to be passed on to the shaping network 184. The 22 microfarad condenser 186 quite readily passes all th frequencies in the range under consider tion of one-fourth cycle" per second upward. The primary condenser 187, together with that part of the inductance of auto-transformer 189 with which it is effectively in circuit, is most selective to frequencies of apprbximately one and one'half times the signaling frequency. This means that the circuit While critically damped offers slightly higher impedance to frequencies of'one and one half times the signaling frequency than to those below but considerably lower impedance to high interfering frequencies. Consequently it tends to even up the unequally attenuated frequency components. The large resistance tude necessary for critical damping. The

magnitudes of the primary'of the autotransformer 189 and the adjustable resistance 188 are based on a compromise between conflicting conditions. The resistance, it may be said,sl1ould be large enough in relation to the reactance of the primary of the auto transformer 189 so that the phase shift between different frequency compo- 188 is preferably several times the magninents is negligible with respect to effect upon the shape of the signal wave, over that frequency range in which the auto-transformer is effective in producing a discrimination in favor of the higher frequencies. The transformer has no effect for direct current and little effect for the very low frequencies. Its effect increases relatively with frequency until a point beyond the range of interest, for example, zero to 150 cyclesat which the distributed capacity of the coil begins to cut down the transformerefiect. The time interval between a signal component of a certain frequency at the secondary terminals and a signal component of an- .other frequency, is substantially the same as the time interval between these signal components at the primary terminals over the greater part of the range of frequencies for which the auto-transformer is effective in increasing the voltage, or, looked at from the point of view of changes in phase angles rather than intervals expressed directly in time units, the components of the signal voltageappearing at the secondary terminals are retarded in phase relatively to the same components of the signal at the primary terminals by an angle which is approximately proportional to the frequency of the components. The resistance should of course be large enough to render the se lective circuit 184, including the primary inductance, non-oscillatory, but this condition will usually be met if the preceding requirement is fulfilled. For the inductance it may be pointed out that the amplifier plate circuits are high impedance circuits and it is desirable to have a reasonable por tion of the output voltage of the first stage amplifier 6A1 made available for the second stage amplifier 6A2. Accordingly, the primary of the auto-transformer is given a value of 50 to 200 henrys. Then, in order to get a large step-up voltage of low frequency currents, the turns ratio of the autotransformer is made very large. As previously indicated, resonant or highly oscillatory circuits must be avoided and the 2 me ohm resistance 190 helps the loop inclu ing the .001 microfarad secondary condenser 192 to meetthis condition. The selectivity of the loop including secondary condenser 192 is such as to make its highest voltage fall at a point approximately one and one half times the signaling frequency, but notat the same point as the first or primary condenser loop 184. Neither loop is oscillatory since the resistance 188, which is usually between-100,000 and 200,000 ohms in value, prevents oscillation in the first loop and the two megohm resistance 190'together with the resistance of the primary loop 184 "with which it is coupled, makes the second loop non-oscillatory. The principal difficulty encountered .in constructing this apparatus was the design of an inductance coil for the auto-transformer 189. Asprevious- 1y stated, this coil must have a high step-up ratio and a primary inductance of 50 to 200 henrys. The difliculty in designing such a coil is to get these high values of inductance with sufliciently low distributed capacity. A suitable design of coil is referred to hereinafter.

The last two networks 193 and201 are similar to elements of a low pass filter. By making the, inductance element and the resistance element variable, either may be used aloneif it is found desirable. An inductance element is preferred, and it may be desirable to use the resistance in parallel therewith to control the damping of the circuit, Each network consists of an inductance coil connected in series with the signal transmission circuit and a condenser connected in shunt across the circuit. Looking at the circuit in another way the incoming transmission line or circuit is terminated in an inductance element and a capacity element connected in series. The outgoing transmission line or circuit is then connected directly to the terminals of the capacity element. By suitable adjustment of the inductance and capacity elements this circuit, may be made primarily effective to transmit a desired frequency which may be essential to signaling. By the proper proportioning of the resistance of the inductance element, the circuit may be made less effective to neighboring frequencies by any desiredamouut. The resistance is usually made large, so as to give a flat selective characteristic of desired shape. A material advantage of this arrangement is the relatively sharp cut-off provided at the up- 1 per limit of the desired frequency range.

Referring now to Fig. 8, which shows a two-way mid-line duplex repeater, two sec tions of cable 230 and 231 are connected through duplex bridge circuits by repeaters ER and VVR. The bridge arms 232 are each of 600 ohms resistance, but might in another case consist of condensers of about 50 mf. each. In this latter case condenser 262 would be omitted. The cable sections 230 and 231 are balanced by artificial cables 233 and 234 respectively. Connected to the conjugate points of the duplex bridge M through an artificial line 236 and shaping network 237 is a shielded bridge transformer 235.

The artificial line 236 is of the balanced type consisting of ten sections, each section consisting of resistances 238 and 239 each of 30 ohms and condenser 240 of 6.9 microfarads capacity. This artificial line functions to transmit the frequencies involved in signaling but suppresses the higher frequencies. The ratio of output to input currents for this line-at different frequencies is out out by theartificial line.

.235 to increase the efficiency of the system.

approximately as follows: 10 cycles, .32; cycles, .2; 50 cycles, .077; 100 cycles, .026; 200 cycles, .006; 400 cycles, .0007.

The artificial line 236 which, as will be seen from the data just given, causes a decrease in the strength of the signaling current, permits the use of an input transformer 235 whose windings are imperfectly shielded and not at all balanced to the shield. This results in an unbalance to ground, which, being a complex impedance varying with frequency, cannot be balanced by any method. The Wave caused bythis unbalance consists mainly of relatively high frequencies which are nearly completely It is to be understood that the specially balanced transformer described in connection with Fig. 4 can be used in place of the artificial line 236 and partially shielded transformer A-shaping netwofk 237 connected across the primary of transformer 235 consists of in- I; ductance coil 241 of 1 to 2.5 henrys and a resistance 242 of zero to 100 ohms. Inductance coil 241 consists of 1500 turns of No. 19 black enameled silk covered copper wire wound upon a toroidal core. The core consists of finely divided iron in the form of rings. This material is described in an article by Buckner Speed and G. WV. Elmen entitled Magnetic properties of compressed powdered iron, which ,Was published in the Journal of the American Institute of Electrical Engineers for July 1921.

Thirty rings each 3 inches inside diameter and 5 inches outside having a permeability of approximately 55 make up the core. Taps are made at 1,000, 1,100, 1,200, 1,300 and 1,400 turns.

The secondary winding of transformer 235 is connected to potentiometer 243 of one megohm resistance. The intermediate point.

of potentiometer 243 is connected through an inductance coil 244 of 1.5 milli-henrys and negative polarizing battery 246 of 1 volts to the id of implifier 8A1. A condenser 245 of l001 mf. capacity is connected from a point between the inductance 244 and battery 246 to the filament of amplifier 8A1. Similar inductances and condensers are connected to amplifiers 8A2 and 8A3. These elements function to prevent pick-up interference as hereinbefore described.

The coupling between stages of amplifier ER is similar to that of the amplifier of Fig.

5. Consequently, only the values of the cir-' cuit elements need be given. Inductance coil 270 has a permalloy core and an inductance of 30,000 henrys. Resistance 247 is of 5,000 to 200,000 ohms. Battery 8B1 is of 220 volts. Condenser 248 is of .001 microfarads maximum capacity. Condenser 249 is of 9 microfarads capacity. Leak resistance 250 between each of the stages is two megohms.

The inductance coil 251 is of 30,000 henrys inductance. Resistance 252 is of the order of 100,000 ohms. Condenser 253 is of .001 microfarads maximum capacity. Condenser 254 is of 10 microfarads capacity. Coil 255 is of 760 henrys. is of 1,000 to 6500 ohms. Resistance 257 is of 50,000 ohms. Condenser 258 is of.03 microfarads. maximum capacity. Condenser 259 is of 10 microfarads capacity. Inductance coil 260 is of 28 henrys. Resistance 261 is of 45 to 900 ohms. Condenser 262 is of 120 inicrofarads capacity and is used to insulate the amplifier from'the duplex bridge N. Battery 8B2 is of 250 volts, battery 8B3 is of 200 volts and battery 8B4 is of 240 volts. Negative polarizing battery 263 is of three volts, battery 264 is of 10 volts and battery 265 is of 50 volts. The filaments are heated from battery 266 of 8 volts. The output circuit of amplifier 8A4 is connected through condenser 262 to the apex of duplex bridge N.

For repeating in the o posite direction, the conjugate points of duplex bridge N are connected through an artificial line 267 similar to artificial line 236, network 268 similar to network 237, transformer 269 similar to transformer 235 and repeater WR similar to repeater ER.

The preferred vacuum tubes for the arrangement of Fig. 8 are those manufactured by the Western Electric Company, Incorporated. One designated as No. 209A is used for each of amplifiers 8A1 and 8A2. Two designated as No. 208A connected in parallel are used for amplifier 8A3 and eight designated as No. 208A connected in parallel are used for amplifier 8A4.

The circuit elements of the two branches of the two-way repeater of Fig. 8 have been described as bein In certain cases t ey may be identical. In other cases it is preferable to adjust them for most efficient operation at different Resistance 256 similar to one another.

dency of the amplifier to sing. The amplifiers of each branch are adjusted to give maximum gain for currents of certain frequencies dependent upon the signaling frequency. In the usual case maximum gain occurs at about one and one half times the signaling frequency; therefore if the speed of signaling in both directions is the same the point of maximum gain in both amplifiers will occur at the same frequency. The net gain of each amplifier at this frequency must be kept low enough to prevent singing. By employing different signaling frequencies in opposite directions the maximunrgain in the quency components.

diiferent amplifiers occurs at different frequencies. The net gain of each amplifier can therefore be increased and still maintain the same singing margin at any given'frequency. Such as adjustment of the amplifiers is contemplated by this invention.

It should be noted that it is not desirable to adjust the shaping elements of the repeater so that the received signal is made legible and retransmitted in this condition, since this involves the production of a large proportion of very low frequency components of the signal wave which must in any case be suppressed at the receiving end of the second cable. The preferred method is to adjust therepeater so that the high frequency components of the signal are amplified as much as possible while the lower frequency components are amplified in a much smaller degree. The retransmitted wave is consequently illegible at the sending terminal of the second-cable, because of-the superabundance of the high frequency signal components, but the second cable at; tenuates the higher frequencies so much more than the lower frequencies that the signal at its receiving end is illegible because of the preponderance of the lower fre- The shaping elements in the receiver correct this condition by selectively amplifying the high frequencies more than the lower frequencies, and also making the necessary phase corrections.

A type of bridge transformer which is suitable for use -in the arrangements hereinbetore described is shown in Figs. 9, 10'and 11. A core 300 consisting of permalloy strips is built up in the manner shown with a small air gap. The primary winding .consists of four pancake sections 301 each 0.25 inch thick and containing 750 turns of No.

, 27 black enamel covered copper wire having a resistance of 27 ohms per section or a total resistance of 108 ohms and an inductance of 225 henrys. The secondary winding 302 consists of one inch pancake coil having 5,000 turns of No. 40 single silk covered copper wire. The primary winding is di vided into two-sections each enclosed in a copper shield 303. The secondary coil is also enclosed in a copper shield 304 and is located on the central leg of the core between the two sections of the primary winding. A lead 305 is taken ofi of each copper shield at a point which is symmetrical with respect to a slotv 306 in the shield. The primary I shields are connected to one terminal of the primary winding, as shown in Fig. 4,- and the secondary shield is grounded, as shown in the same figure. Care must be exercised to maintain perfect insulation between the shields and the windings, the shields and the cores and between the primary and secondary shields.

A type of co11,'whichis suitable' for autotransformer 189 of Fig. 6 has a. core si'nilar to that'ofj'the bridge transformer described in connection with Figs. 9, 10 and. 11, in which a small air gap is included in the magnetic circuit at one end of the central leg. The winding consists of 7 pancake sections, each .35 inch thick and containing 8300 turns of No. 40 single silk covered copper wire having a resistance of about 6500 ohms per section. The total copper resistance is of the order of 50,000 ohms and the total inductance approximately 6,000 henrys.

An arrangement especially suitable for high speed signaling on a loaded submarine cablevis that shown in Fig. 6, modified according to Fig. 12. At the receiving terminal, cable 5 is connected to an intermediate point of auto-transformer 358, through condenser 355 of 2 to 20 microfarads capacity and resistance 356 of 500 to 100,000 ohms. The total inductance of auto-transformer 358 is from 1 to 15 henrys, while the inductance of that portion between the lower terminal and the intermediate point is from one quarter to 2 henrys. Condenser 355 and resistance 356 are necessary only at the highest signaling speeds, and may be effectively elim-. mated by the closure of switch 357. By

means of switch 362, a condenser 360 of .5 to i 10 mf. capacity shunted by resistance 361 of to 5,000 ohms may be connected between the intermediate point of auto-transformer 358 and ground to eliminate high frequency disturbances when these are excessive. Across the network 366, which consists of auto-transformer 358 and resistance 359, is',

this condenser and the resistance 365 is from 3 to 10 seconds, that is, the capacity in microfarads multiplied by therlresistance in megohms equals 3 to 10. In cases where earth currents necessitate this condenser, re-

sistance 365 would be increased to the order of100,000 ohms in order to permit the use of a condenser of moderate size. The function of the networks 184: and 193 and 202 of Fig. 6 have been described hereinbefore. The function of the network 366, consisting of auto-transformer 358 and resistance 359, which serves to terminate the cable, will now be described. The action of network 366 is to transmit from the cable to the first stage amplifier 6A1 components of all frequencies, I

the voltages of the higher frequency com ponents being steppedup more than those of the lower? 'The resistance 359 insures a difference of potential between the cable terminal and ground even at zero frequency (direct current).

The arriving currents in passing through the portion of the network 366 to ground encounter an impedance which increases with increasing frequency. The change in impedance is due primarily to change in reactance, since the resistance of this path does not greatly vary for the different component frequencies. Each frequency component of the primary current will therefore experience a slightly different phase shift from that of any other frequency component. At the point where the reactance and resistance are of equal magnitude, the phase shifts rapidly with slight changes in either magnitude. If either the reactance or the resistance greatly preponderate, the shift in phase for a change in either magnitude is relatively less. The primary circuit of the network 366 is accordingly made the principal phase shifting device, and its constants are so designed as to make the front of the arrival curve as steep as is necessary to reproduce the highest frequency components of the signal.

The four functions of the network 366 are:

1. To terminate the cable with proper impedance.

2. To correct relative phases of the components which make up a signal impulse.-

3. To step up the voltages of the incoming frequency signal components.

4. To perform some attenuation correction by stepping up the voltages of the higher frequencies more than the lower.

The first function determines the total magnitudes of the primary impedance of the network 366. If, for-example, the cable is of 4.00 ohms impedance at the signaling frequency the network 366 viewed from the cable terminal and ground should be ofcomparable impedance in order to satisfy the well-known principle of matching impedances of coupled circuits.

The relative magnitudes of the resistance and inductance elements to accomplish the second function may be determined experimentally. 1

The fourth function, namely, the attenuation corection depends upon having the turns ratio of the coil sufficiently large to accomplish this function. To secure such a coil, magnetic cores are essential, and a material such as compressed owdered iron (-see the articleby Messrs. peed and Elmen supra), which gives a resistance and inductance substantially independent of current and frequency, is best. The actual total magnitude of the inductance depends, in v the first place, on the primary portion magnitude (set by function 1), and in the second place upon the step-up of the voltage that is desired. \Vith a signaling frequency of 60 cycles a total inductance of the order of 1 henry, with the turns about equally divided, and with approximately 15 ohms resistancein series is suitable for terminating a loaded cable having 400 ohms impedance.

Potentiometer 365 merely permits poten tial regulation.

While it is preferable that all of the required phase shifting be done by network 366, each 'of the networks 61 and 184 may function to acomplish both phase shift and attenuation correction, but in different relative amounts in order to properly shape highly distorted signals such as maybe received from an inductively loaded cablefor example, a cable loaded with a nickeliron alloy of high permeability, such as cable 5 in Fig. 12.

As was indicated in the description just given, the signal adjustment of the various elements will vary under different conditions, and can best be determined by observing the form of the received signals, and it is evident that considerable skill and time is required to adjust cable telegraph signal amplifying apparatus so that the wave form of the signaling current may be suitable for receiving purposes.

In most cases the selective circuits, such for example as networks 99, 100 and 101 of Fig. 4, are so highly damped as to be nonoscillator-y. In certain instances it may be advantageous to permit them to be resonant, in which case it is desirable to make each succeeding network proceeding in the direction of transmission resonant to a frequency higher than that to which the preceding network is resonant. Thus network 100 would be resonant to a frequency higher than that of network 99 and network 101 to a frequency higher than that of network 100'.

From the foregoing description modifications coming Within the urview of the invention will be obvious. uch modifications therefore come within the scope of the ap- 'pended claims.

What is claimed is- 1. In submarine cable. telegraph terminal apparatus,signal shaping means comprising two shaping units each unit producing both a relative phase shift and unequal attenuation of the component frequencies of the signal current, the proportional effects being different in each of the units, and signal .identifying apparatus electrically connected to said shaping units.

2. In submarine cable telegraph terminal apparatus, signal shaping means comprising one shaping unit for producing primarily a relative phase shift of the component frequencies of the signaling current and a second unit for producing unequal attenuation of said component frequencies without producing such phase shift thereof as to materially'affect the sh. e of the signal impulses, and signal i entifying apparatus electrically connected thereto.

3. In terminal apparatus for submarine cable telegraph signal which .comprises first shifting the relative phases of the frequency components of the received wave until they together most nearly form a rectangular shaped wave, and subsequently varying the relative amplitudes of said components to cause a rectangular wave form to be still further approached.

5. In a submarine cable telegraph system, a submarine cable, means, discriminating between signal components of certain frequencies and other frequencies present in the system, for transmitting signaling currents impressed thereon without producing such relative phase shift of the component frequencies thereof as to materially affect the shape of the signal impulses, and a phase shifter between said means and said cable for effecting the phase shifts necessary to reproduce the signal.

6. In a submarine telegraph cable system, a submarine cable, a network which is effective to relatively shift the phase of the component frequencies of the signaling current to the extent necessary to reproduce the signal and which also partly corrects for undesired relationship of amplitudes of said components, a separate network for completing the amplitude correction, and means between said networks for preventing reaction of the succeeding one upon the precedin one.

7. n a submarine telegraph cable system, a submarine cable, and signaling apparatus therefor comprising a wave shaping autotransformer, the resistance of the primary circuit hem of such valuethat the transformer is e ective to shift the relative phase of the frequency components of the impressed wave until they together most nearly form a rectangular shaped wave.

8. The combination with a submarine cable havin an inductively loaded telegraph conductor, of terminal shaping means comprising a shaping unit for compensating principally for the unequal phase shifts caused by the cable and in part by the load' ing, and a second shaping unit for compem;

sating principally for unequal attenuation of the frequency components of the signal by the cable.

9. The combination with a submarine tel aph signaling conductor, of inductive 103. g therefor consisting of nickel-iron alloy of high permeability, and terminal shaping means comprising a shaping unit for compensating principally for unequal phase shifts of said components by the cable and in part by the loading and a second shaping unit .for compensating principally for unequal attenuation of the frequency components of the signal by the cable.

10. In terminal apparatus for submarine cables inductively loaded with a nickel-iron alloy of high permeability, signal shaping means comprising one shaping unit for producing a major portion of the total relative phase shift of the component frequencies of the signaling current which is required for shaping the signal impulses for signal identification, and a second unit for producing unequal attenuation of said component frequencies without producing such phase shift thereof as to materially affect the shape of the signal impulses, and signal identifying apparatus electrically connected thereto.

11. In a submarine cable telegraph system, a submarine cable inductively loaded with .a nickel-iron alloy of high permeability, means for amplifying signaling currents impressed thereon, without substantial relative phase shift of the component frequencies thereof and an auto-transformer connected between said cable and said means to effect desired relative phase. shift between the frequency components of the signaling current.

12. In a submarine cable telegraph system, a submarine cable, an amplifying device for amplifying signaling currents impressed thereon, without substantial relative phase shift of the component frequencies thereof and an auto-transformer connected between said amplifying device and said cable to effect desired relative phase shifts between the frequency components of the signaling current.

13. In a submarine cable telegraph system, a submarine cable, an electron discharge amplifying device for amplifying signaling currents impressed thereon without substantial relative phase shift of the component frequencies thereof, and a voltage amplifying auto-transformer which is more effective for the higher frequency components of the signaling current than for the lower frequency components, the low voltage terminus tem, a submarine cable, an electron discharge amplifying device for amplifying signaling currents impressed thgeon, without sub- .stantial relative phase shift of the component frequencies thereof and a voltage ampliing auto-trans'formenwhich is more effective for the higher frequency components of the signaling current than for the lower frequency components, and which has a primary rseistance of such value that the transformer is primarily effective to relatively shift the phases of the component signaling frequencies, the low voltage terminals of said transformer being connected to the cable and the high voltage terminals to the electron discharge amplifying device, whereby desired relative phase shifts between the frequency components of the signaling current may be effected.

15. In a submarine cable telegraph signaling system, a submarine cable, a network comprising an auto-transformer which is primarily effective to relatively shift the phase of the component frequencies of the signaling current, a second network for relatively varying the amplitudes of the component frequencies of the signaling current without relatively so shifting their phases'as to materially affect the shape of the signal impulses and a unilateral translating device connected between said networks to prevent reaction therebetween.

16. In a submarine cable telegraph system, a cable which attenuates the higher frequencies essential to signaling more than the lower frequencies, and a signal shaping system which functions also to transmit frequencies within the range involved in signaling more efficiently than certain frequencies somewhat above said range and other frequencies somewhat below said range.

17. In a' submarine cable telegraph system, a cable which attenuates the higher frequencies essential to signaling more than the lower frequencies, and a plurality of shaping means separated by means which prevents reaction of a succeeding shaping .means upon a preceding shaping means, said shaping means as a whole acting also 'to transmit frequencies within the range involved in signaling more efficiently than certain frequencies somewhat above said range and other frequencies somewhat below said range.

18. In a submarine cable signaling system, a submarine cable, a signal transmission circuit including said cable, an induc tive element connected in series with said circuit and a capacity element connected in shunt of said circuit, the inductance of said inductive element and the capacity of said capacity element being so proportioned .that the circuit transmits most efiectively current of a frequency within the range of frequencies essential to proper shaping of the signals, and less effectively by any desired amount currents of neighboring frequencies, v

19. In a submarine cable signaling system, a-submarine cable, a signal transmission circuit including said cable, an inductive element connected in series with said circuit and a capacity element connected in shunt of said circuit, the inductance of said network comprising an inductive element connected in series with said circuit, and a capacity element connected in shunt of said circuit, the inductance of said inductive element and the capacity of said capacity element being so proportioned that the network transmits most effectively current of a frequency within the range of frequencies es sential to proper shaping of the signals and less effectively by any desired amount currents of neighboring frequencies, and a second selective network comprising an inductive element connected in series with said circuit and a capaclty element connected in 'shunt of said circuit, the inductance of said inductive element and the capacity of said capacity element being so proportioned that the network transmits most effectively currents of a frequency outside the range of frequencies essential to proper shaping of the signals and less effectively by any desired amount currents of neighboring frequencies.

21. A submarine cable telegraph receiving apparatus for receiving signals which have been distorted in amplitude and phase, comprising si nal shaping means having a plurality of s aping units in which the proportional correcting effects on amplitude and phase of one of said units are different from those of another of said units and one of'said units produces primarily unequal attenuation of said component frequencies.

22. In a signaling system, a signal aniplifier consisting of a plurality of electron discharge devices each having a cathode, an anode and an impedance controlling electrode, means to impress upon the impedance controlling electrode and cathode of one of said devices signaling current having components of frequencies involving a frequency range of several octaves, a highly damped selective circuit for transmitting said current comprising inductance, resistance and capacity elements. means for connecting the anode and cathode of said device to said highly damped selective circuit-,and other means to connect the grid of a second electron discharge device to one terminal of said condenser and the cathode to the'other terminal.

23. In a submarine cable signaling system, a submarine cable, means to ampress signal- "ing impulses upon said cable, at one end, a

frequencies of several octaves from the output circuit of said first device upon s'aidinductance, and means to connect the input circuit of a second device across said condenser.

24. In a submarine cable signaling system, a submarine cable, means to impress signaling impulses upon said cable at one end, a signaling amplifier comprising a plurality of electron discharge devices each having an input and an output circuit, means to impress signaling current received from said cable upon the input circuit of one of said devices, a highly damped selective circuit comprising inductance and capacity elements, means-to impress current from. the outputcircuit of said first device upon said inductance, means to connect the input circuit of a second of said devices across said condenser, and means to adjust the reactive elements of said selective circuit so that the potential drop across said condenser is a maximum for currents of a frequency within the range of frequencies essential to signal- 25. In a signaling system, a multi-stage signal amplifier, means to impress signaling current upon one stage thereof, a selective circuit comprising inductance and capacity elements connected between one of said stages and a succeeding stage and effective to cause a greater amplification of certain frequencies than of others, and a second selective circuit comprising inductance and capacity elements connected between said succeeding stage and another succeeding stage and effective to cause a greater amplification of certain frequencies of higher value than those efiected by said first mentioned selective circuit.

26. In submarine cable telegraph terminal apparatus a signal shaping element consisting of an auto-transformer with a resistance added to its primary circuit, the proportion of the resistance, primary inductance and turns ratio of said auto-transformer be ing such that over a certain range of frequencies the. ratio of voltage transformation increases as the frequency is-increased, and

the time interval between a signal component of a certain frequency at the secondary terminals and a signal component of another frequency, is substantially the same as the time interval between these signal components at the primary terminals, over the greater part of the range of frequencies forwhich the auto-transformer is effective in increasing the voltage,

27. In submarine telegraph terminal apparatus a signal shaping .element consisting of an auto-transformer with a resistance added to its primary circuit, the proportions of the resistance, primary inductance and turns ratio. being such that over a certain range of frequencies the ratio of voltage transformation increases as the frequency is increased, and the components of the signal which appear at the secondary terminals are retarded in. phase relatively to the same components of the signal at the primary terminals by an angle which is approximately proportional to the frequency of said components.

28. In a submarine cable signaling system, a duplex bridge arrangement, means to connect sending apparatus between the apex of said bridge and earth, 'a bridge transformer having a'primary and a secondary winding, means to connect the primary winding to the con ugate points of sald duplex bridge, means to connect said secondary winding to an earthed receiving circuit, an electrical shield surrounding said primary winding and connected to one terminal of said primary winding, and a second electrical shield surrounding said secondary winding and connected to earth.

29. In a submarine cable signaling sys tem, a duplex bridge arrangement, means to connect sending apparatns'between the apex of said bridge and earth, a bridge trans former having a primary and a secondary winding, a core for said. transformer consisting of permalloy, means to connect the primary winding to the conjugate points of said duplex bridge,-'means to connect said secondary winding-to an earthed receiving circuit, an electrical shield surrounding said primary winding and connected to one ter-. .minal of said primary winding, and a second electrical shield surrounding said secondary winding and connected to earth.

30. The method .of duplex telegraphy.

which comprises transmitting superposed signals simultaneously in opposite directions, separately amplifying the currents corresponding to the oppositely transmitted sigals, and transmitting at different speeds in the two directions in order to preventinterference between the oppositely directed signals.

31. In a cable signaling system, two sec- 

